HR: 17:45h
AN: V34B-08 INVITED     [Abstracts]
TI: Hawaiian Hotspot - Spreading Ridge Interaction in the Late Cretaceous: A Fair and Balanced Look at the Evidence
AU: * Keller, R
EM: rkeller@coas.oregonstate.edu
AF: College of Oceanic & Atmospheric Sciences, Oregon State University, Corvallis, OR 97331
AB: As is so often the case in years divisible by 4, reality turns out to be quite different from reputation. The Hawaiian hotspot, often righteously promoted as the hotspot that the rest should strive to emulate, was not as stable nor as free from interactions with plate boundaries as some supporters suggest. Mounting geochemical and geophysical evidence shows that in its youth the hotspot not only inhaled, but probably snorted and did shots as well. The purpose of this presentation is to summarize what we know about the Late Cretaceous interaction between a spreading ridge and the Hawaiian hotspot from recent work on the Emperor Seamount chain. At the time of this writing, facts are a commodity to be fabricated, deleted, spun, denied, and denied-that-you-denied; but by the time of this presentation, we (hopefully) will be looking toward the future: can the Hawaiian hotspot's checkered past be treated as a bonus rather than a burden? Plate reconstructions of the Late Cretaceous northwest Pacific place a seafloor spreading center very close to, or even directly on top of, the Hawaiian hotspot. The geochemical effects of this hotspot-ridge interaction are now well documented by work on Ocean Drilling Program samples from Detroit Seamount, the next-to-oldest remaining Emperor Seamount. Basalts recovered from ODP Site 883 partway up the east side of Detroit Seamount have trace element and isotopic characteristics more akin to MORB than to Hawaiian Islands basalts. Basalts from ODP Site 884 at the eastern foot of the seamount are highly depleted tholeiites unlike anything else found so far in the Hawaiian-Emperor chain (Keller et al. 2000, {\it Nature}). Their trace element and radiogenic isotope values are essentially indistinguishable from MORB values (Keller et al. 2000), although triple-spike Pb isotope data are distinct from modern EPR MORB data (Regelous et al. 2003, {\it J. Pet.}). These characteristics were the result of the hotspot melting a greater proportion of a depleted mantle component, whether entrained from the surrounding upper mantle (Keller et al. 2000) or intrinsic to the plume (Regelous et al. 2003), while it was close to the spreading center. The Site 884 basalts are surprisingly old (81 Ma; Keller et al. 1995, {\it Leg 145 Sci. Results}) in comparison to recent results for Site 1203 basalts from near Site 883 (76 Ma; Duncan and Keller 2004, {\it G-cubed}). The unique composition and surprisingly old age of the Site 884 basalts could be due to the fact that we have not drilled a similar location deep on the flank of another Hawaiian hotspot island or seamount. However, my preferred explanation is that the temporal and spatial distribution of hotspot volcanism was also influenced by the nearby spreading center. A modern analog for Detroit Seamount may be a complex seamount platform similar to the Gal\`{a}pagos hotspot-ridge system.
DE: 9355 Pacific Ocean
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 1035 Geochronology
DE: 1040 Isotopic composition/chemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting